Recent years have seen a great expansion in the complexity of consumer electronics equipment with several different proprietary and technical standards governing interconnectivity and data storage. In connection with the latter feature, the domestic user has in the past used different mechanical and functional configurations of storage device, such as a VHS cassette for video recording, an audio compact cassette for audio recordings from Hi-Fi equipment, and hard and floppy discs for data storage on personal computers. With the advent of recordable optical discs conforming to unified standards as far as data layout, bit rates etc. are concerned, such discs may (if configured to the particular recording system) replace many of the disparate options, and hence the possibility of a single unified standard, both in terms of physical configuration and data management, may be contemplated for all types of domestic audio/video/data-processing systems.
In conjunction with this increased commonality in the field of storage media, there is an increasing degree of requirement for sharing in the expected and actual functionalities of the devices themselves. Of particular relevance to the present invention is the digital recording of audio and/or video (AV) material, with the user coming to expect the same sort of facilities for arranging and editing of stored data that they experience from, for example, a personal computer. In terms of available devices, optical media were not particularly suited for video storage applications due to their hitherto limited storage capacity, although this is becoming less of an issue: for example, a disc according to DVD-ROM standards may store in the region of 8 hours of video compressed following MPEG2 protocols. Further developments are providing optical drives with a capacity of tens of gigabytes per storage device (disc) and real-time video recording applications based around such storage devices are contemplated.
Whilst many efficient schemes have been proposed for recording and storage of program data, it will be understood, however, that there are constraints to be observed in the storage of AV material which differ from those applied in the generation of efficient file structures and file handling in a purely data-oriented environment. Of particular relevance is the system-imposed desire for sections of video data (which may be interleaved with data for an accompanying soundtrack) to be stored contiguously such as to enable the encoded video data to be read fast enough to avoid presenting visible discontinuities to the viewer—for example to meet the applicable buffering constraints where the video data is MPEG encoded.
Inefficient storage file structures can lead to problems in these areas and a number of strategies have been proposed for enhanced efficiency in is multimedia data storage and retrieval, particularly for magnetic disc storage, as described in “Multimedia file systems survey: approaches for continuous media disk scheduling” by Ralf Steinmetz, Computer Communications Vol. 18, No. 3, March 1995 pp. 133-144. As is mentioned by Steinmetz, it is possible for data to be shared between files, a particular example of which would be different versions of a stored file (e.g. a censored children's version and an adult uncut version of a film) on a single disc with simple re-use of common sections of data where appropriate to avoid the need for storing full-length but only slightly different versions of a file. At present however, insofar as the idea of re-usability of data has been concerned, it has been based on media where the data is subdivided into convenient uniform segments (for example sectors on a recordable disc) with sharing of file sections only being supported at the segment level. The result of this has been that either edited versions of a file are forced to include whole segments when only a small part thereof may have been desired, or the segment size has to be very small to permit flexibility in editing operations, which is both wasteful of disc space and creates an unacceptably high processing overhead.